A Lamp is a very important apparatus for human civilization life. With development of technology, multiple lamps are designed and manufactured to meet multiple requirements.
With the progress of light Emitting Diode (LED) technology and decline in cost, light emitting diode manufacturing lamps increasingly popular to people's daily lives. Most of white LEDs are currently produced through coating a layer of yellow phosphor on a blue LED (near-UV, wavelengths 450 nm to 470 nm). The yellow phosphor usually obtained by mixing cerium doped with cerium Aluminum garnet (Ce3+:YAG) crystals, and grind the mixture, mix them in a dense adhesive. When the LED chip is blue, part of the blue light will be very efficient conversion of the crystal into a broad spectrum (spectral center is about 580 nm) mainly yellow light. As the yellow light may stimulate red and green light in the naked eye, and then mixed with the blue LED, making it look like white light, and the color is often called “moonlight white.” The method of making white LEDs was developed by Nichia Corporation and used in 1996 to produce white LEDs. To adjust the color of light yellow light, other rare earth metal terbium or gadolinium may be used to replace cerium (Ce) doped with Ce3+:YAG, or even to replace part or all of aluminum in YAG. Based on the characteristics of the spectrum, red and green objects in the LED irradiation may not look like the broad spectrum of light when the light so clear. In addition, due to the variation of production conditions, the color temperature of the finished product of the LED is not uniform, differing from warm yellow to cold blue, so the production process may be distinguished by outcome characteristics.
Another method of making white LED is a bit like a fluorescent lamp, emitting near ultraviolet LED may be coated with two kinds of phosphor mixture, one is red and blue light europium, the other is green, doped with copper and aluminum of zinc sulfide (ZnS). Because the UV may make the adhesive in the epoxy resin cracking deterioration, production is more difficult, and life is shorter. Compared with the first method, it is less efficient and produces more heat (because former Stokes shift is larger), but the advantage is better spectral characteristics, producing the better look light, and because the UV light LED power is high, so the efficiency is relatively low compared to the first method, but the brightness is similar.
The latest method of making white LEDs is no longer used phosphors. The new approach is to grow the epitaxial layer of zinc selenide on zinc selenide (ZnSe) substrates. The active area emits the blue light and the substrate emits yellow when connecting the power, and then mixing together becomes white light.
There are some different technical problems have to be solved in the different light emitting diode lamps, including heat dissipation, light efficiency and light emission direction. In addition, if it may further reduce the cost of manufacturing may also help to increase the popularity of the light emitting diode lamps in human society.